docs: def correlation_plot(self, data):
          """ Create heatmap of Pearson's correlation coefficient.
  
          Parameters
          ----------
          data    : pd.DataFrame()
              Data to display.
  
          Returns
          -------
          matplotlib.figure
              Heatmap.
  
          """
  
          # CHECK: Add saved filename in result.json
          fig = plt.figure(Plot_Data.count)
          corr = data.corr()
          ax = sns.heatmap(corr)
  
          Plot_Data.count += 1
          return fig